Derivatives

massless

Even though photons are massless, they still have an equivalent mass because they have energy.

For example, Einstein's special relativity theory predicts that massless particles in a vacuum travel at the speed of light and that particles with mass travel more slowly, in a way that can be calculated if we know their mass.

Origin

There is no relation at all between late Middle English mass ‘a large body with no definite shape’ and Old English Mass ‘the celebration of the Christian Eucharist’. The first goes back to Greek maza ‘barley cake’. The other derives ultimately from Latin mittere ‘to dismiss, send’, and so is connected with message, missive (Late Middle English), and amass (Late Middle English), as well as with words such as permit. The use for the religious service may come from its last words in Latin, Ite, missa est ‘Go, it is the dismissal’. Ordinary people have been called the masses since at least 1837, and they have been supplied with goods by mass production since 1893.